Styrenic resins having .alpha.,.beta.-unsaturated carboxylic acid moieties incorporated therein have long been known to be useful plastics for the production of molded articles having good heat resistance. However, these materials tend to be rather brittle, decreasing their utility in end-use applications wherein they will be subjected to repeated impact or flexing. A common solution to this problem is to incorporate a high molecular weight hydrocarbon-based rubber or elastomer such as a butadiene-containing polymer into the styrene resin so as to improve the toughness and impact properties. Although this approach works well and is practiced commercially on a large scale, it suffers from the disadvantage that the styrenic resin is typically rendered opaque (non-transparent) by the introduction of the rubber. In certain applications such as packaging, however, a non-brittle clear resin having good flexibility and resistance to cracking would be highly desirable. Currently available impact-modified styrene/carboxylic acid moiety copolymers are generally not suitable for such uses.